Insulated wires, cables, and cords, which are used for inner and outer wiring of electric/electronic equipment, optical fiber cores, and optical fiber cords, are required to have various characteristics, including fire retardancy, heat resistance, and mechanical characteristics (e.g. tensile properties and abrasion resistance).
For this reason, as the covering material used for these wiring materials, a polyvinyl chloride (PVC) compound and a polyolefin compound, wherein a halogen-series fire-retardant additive containing bromine atoms or chlorine atoms in the molecule is mixed, have been mainly used.
In some cases, however, when they are discarded or buried without being treated properly, the plasticizer or the heavy metal stabilizer mixed in the covering material is oozed out, or when they are burned, a corrosive gas is produced from the halogen compound contained in the covering material, in some cases; and in recent years, this problem has become controversial.
Therefore, wiring materials covered with a halogen-free fire-retardant material free from any risk of oozing out of toxic plasticizers or heavy metals, or generation of a halogen-series gas or the like, which involves concern about affecting the environment, are investigated.
Halogen-free fire-retardant materials secure their fire-retardancy by mixing a halogen-free fire-retardant additive in a resin. For example, a material obtained by mixing a large amount of a metal hydrate, such as aluminum hydroxide and magnesium hydroxide, as a fire-retardant additive, in an ethylene-series copolymer, such as an ethylene/1-butene copolymer, an ethylene/propylene copolymer, an ethylene/vinyl acetate copolymer, an ethylene/ethyl acrylate copolymer, and an ethylene/propylene/diene terpolymer, is used as a wiring material.
The standards, for example, of the fire retardancy, the heat resistance, and the mechanical characteristics (e.g. tensile properties and abrasion resistance) required for wiring materials of electric/electronic equipment are stipulated in UL, JIS, etc. In particular, with respect to the fire retardancy, its test method varies depending on the required level (its use to be applied) and the like. Therefore, practically, it is enough for the material to have at least the fire retardancy according to the required level. For example, mention can be made the respective fire-retardancy to pass the vertical flame test (VW-1) stipulated in UL 1581 (Reference Standard for Electrical wires, Cables, and Flexible Cords), or the horizontal test and the inclined test stipulated in JIS C 3005 (rubber/plastic insulated wire test method).
Among these, hitherto, when a halogen-free fire-retardant material is made to have a fire retardancy high enough to pass VW-1 and the inclined test, it is necessary to mix 120 parts by weight or more of a metal hydrate, as a fire-retardant additive, in 100 parts by weight of a resin component, such as an ethylene-series copolymer. As a result, there is a problem that the mechanical characteristics, such as the tensile properties and the abrasion resistance, of the covering material are markedly lowered. To solve this problem, a measure is taken to lower the proportion of the metal hydrate (e.g. about 120 parts by weight of a metal hydrate, as a fire-retardant additive, to 100 parts by weight of a resin), and red phosphorus is added.
Meanwhile, wiring materials that are currently used in electric/electronic equipment, and whose covering material is a polyvinyl chloride compound or a polyolefin compound, wherein a halogen-series fire-retardant additive is mixed, are used by coloring them to be several respective colors, for example, by printing the surface of electric wires, electric cables, and electric cords, for the purpose of distinguishing the types of wiring materials and junctions. However, halogen-free covering materials having a metal hydrate and red phosphorus mixed therein, to secure both a higher fire retardancy and mechanical characteristics, cannot be printed thereon, or they cannot be arbitrarily colored because of the color of the red phosphorus, so that they have the problem that they cannot give wiring materials that allow the types and junctions to be distinguished easily. Further, phosphorus, which will be released after discarding of the fire-retardant material containing phosphorus, poses also a problem that affects the environment; for example, pollution of water by eutrophication.
Further, wiring materials used in electric/electronic equipment are sometimes required to have a heat resistance of 80 to 105° C., or even 125° C., with them being used continuously.
In that case, such a method is taken that the covering material is crosslinked by an electron beam crosslinking method, or a chemical crosslinking method, in order to render the wiring material highly heat resistant.
However, while the crosslinked wiring material is improved in the heat resistance of the covering material, it is impossible to remelt it. Therefore it is pointed out that it is difficult to use said material again, making the recylability thereof poor. For example, when a metal used as a conductor is recovered, the covering material has, for example, to be burned, in many cases, which means that the above environmental problem involving the conventional halogen- or phosphorus-containing covering material cannot be avoided.
On the other hand, as a technique wherein a wiring material having a heat resistance, on the order of 105° C., is realized without carrying out such crosslinking, there is a technique wherein a resin having a high melting point, such as a polypropylene-series resin, is used. However, although such a resin is good in heat resistance, the flexibility is poor, and when the wiring material covered with such a resin is bent, a phenomenon is observed that the surface is whitened.
This whitening phenomenon is not observed in wiring materials currently used in electric/electronic equipment and covered with a polyvinyl chloride compound. On the other hand, in the case of wiring materials covered with a halogen-free fire-retardant material wherein a large amount of a metal hydroxide is mixed, this whitening phenomenon is conspicuous regardless of whether they have been subjected to the crosslinking process or not. Thus, to use the current halogen-free fire-retardant material, which is whitened when bent, for wiring materials, further improvement has been required.
Since the maximum service temperature of a wiring material covered with a polyvinyl chloride compound is on the order of UL 105° C., a halogen-free fire-retardant material for use as a replacement for the wiring material is also required to have that heat resistance. Specifically, since, for a heat resistance of UL 105° C., for example, the heat deformation test and the heat aging test in an atmosphere at 136° C. are required, the halogen-free fire-retardant material, as a replacement, is required to not melt at at least 136° C.
In addition, molded parts, such as power source plugs, have the similar problems as the above, and the development of molded parts has been desired, which have heat resistance, flexibility, and fire retardancy, which can be recycled, and which can be remolded.